Incandescent lamp



Dec. 12, 1939. w. Rbvz 2,182,904 V INCANDESCENT LAMP Filed June 18. 1937 INVENTOR. unthclm var ATTORNEY.

Patented Dec. 12, 1939 v UNITED STATES PATENT: orrics Application June 18, 1937, Serial No. 148,848 W In Germany June 18, 1936 1 (Balm. (Cl. 176-34) This invention r lates to electric incandescent metallic filament, the resistance of which is such lamps adapted-for emergency illumination espethat its temperature remains below 1600 C. cially as a protection agat st visibility by airwhen the lamp is connected to a supply source of craft during emergency alarms and attacks from n rm l pera ng v l M r, the lamp is the air. Y surrounded by a covering or coating consisting of 5 An object of the invention is the provision of a material impervious to light and almost coman electric lamp for emergency illumination p ete y encl sin t e mp bulb except fo a Small whichis substantially invisible when viewed from portion constituting a window for passing the above a predetermined minimum height and, rays of light emitted by the filament. which can be manufactured at cheap cost. There is obtained in this way an ex p n ly It has been found, when the necessity arises of cheap lamp which can be screw d nt any streducing practically to darkness the illumination ing lamp socket without requiring any auxiliaryof streets, squares, houses, etc., during attacks implements and which complies -fully with the from the air, that the light emitted by the lamps conditions and requirem nts during m r n y .should be visible at the most from a height of alarms. Contrary to the known constructions about 300 meters, and that the fiux of light employing a shield or casing for the object stated. emitted from the lamps should not amount to the coating of the present improved lamp is firmmore than about 5 lumen. Furthermore, since 1y connected to the lamp bulb whereby no tracev the visibility depends in the first place on the of light can penetrate to'the outside.

surface brightness per unit of area of a radiating It is of course known that the amount of light body, the incandescent filament itself should not emitted by the filamentof an incandescent lamp be visible either from above or from lateral dimay be-reduced by reducing the temperature of rections. the filament and that furthermore for a given Attempts have been made to obtain the above line voltage a' filament of greater length has a object by covering an ordinary incandescent lamp lower 7 temperature than a shorter filament of g; in a suitable manner, but apart from the fact that equal diameter and consisting of the same matethere always exists the possibility of gaps or open-. rial. These properties have, in fact, already been ings in the fitting elements of the lamp, this exutilized for the manufacture of multi-filament pedient results in an excessive heating of the lamps, the filaments of which have different il- 30 lamp whereby the operating safety and the safety luminating strengths and can be connected selec- 30 against mechanical vibrations may be substantively. tially impaired when they have to be mostly de- It is furthermore old to use the bulb of an in-u pended upon, such as during imminent or actual candescent lamp partly as a reflector. However, air attacks. all these attempts difi'er from the inventive. idea In order to obviate these disadvantages a coatto provide a lamp designed for normal line volting could be applied in direct contact with the age operation with means for reducing the temglass bulb of the lamp in place of a casing or en- .perature of the filament, thereby enabling it to velope and a, low voltage filament could be emprovide directly upon the bulb of the lamp a layer ployed in order to reduce the output of the lamp of lacquer impervious to light rays and insuring to such an e t nt to p v nt x s h atinshigh stability and operating safety as well as free- 40 Such low volta lamps. h wev r, have to be condom from the efl'ects of mechanical shocks. neet d to a lighting circuit through a In order to reduce the heating of the coating former. Moreover, apart from the fact that the of light pervjous t ria th coating may b mployment of such lamps is restricted to alte comprised of two layers, of which the inner one:

a nil-ting rr nt networks wh r y n o he is a reflecting layer for instance a dull white re-nu various voltages used. the d ale s would be fiector while the outer one is black and of light pelled'to keep an und a e number of pes nd absorbing character. The bulb acts then, as it Sizes of l mp on Store, Snell lamps are 1500 were, similar to the spherical reflecting surface pensive to warrant their general introd i n as used in so-called Ulbricht-photometer, the wall 'The improved lamp forming-the subject matofwhich is not perceptibly heated by rays and 50 ter of the present invention is distinguished from from the window of which emanates a very unithe lamps heretofore proposed for the purpose form flux of light. in view by its great simplicity, its extreme free- The invention is illustrated diasrannnatically dom from the effects of mechanical shocks and its and by way of example on the accompanying almost unlimitedlife. The improved lamp has a drawing showing a section through a lamp according to the invention. In the drawing, item B denotes the lamp bulb having the major portion of its outer surface coated with a layer L of a white lacquer upon which coating L there is another coating consisting of a black lacquer, both layers together forming a covering which is substantially impervious to light. Only the spherical cup W opposite the lamp base is left uncoated, thereby providing a window through which the light can escape. If desired, a colored filter may be arranged in front of the uncovered portion or window.

The filament F supported by a re-entrant portion or press P of the bulbB, as regards its sectional area, may be of the type known for the usual 10-watt lamps, with a diameteroi about of l millimeter, and a length about twice the length of the filament of a normal 10-watt lamp, that is consuming only- 5-watt from the same lighting source, and having a temperature amounting only to about 1600 C. The computed life of such a, lamp which can be manufactured "a normal eye from for about the same price as a normal 10-watt lamp is several millions of hours so that the lamp must be considered as unusually safe in service. In addition to its advantage of being substantially shock-proof, the lamp itself and the area sufllciently illuminated by it for carrying on normal manipulations are no longer visible to distances beyond about 200 meters.

I claim:

An incandescent lamp comprising an evacuated bulb of normally clear glass, an incandescent filament mounted therein, a coating of white lacquer applied to the exterior surface of said bulb, a Iurther coating of black lacquer impervious to light overlying said first coating, said coatings covering substantially the major portion .01 said bulb except for a small window, said fllament adapted to maintain an operating temperature below 1600 C. when fed from a lighting circult of standard voltage.

WILHELM Rovm. 

